Electric resistance heating unit



NOV. 4, 1941. EPsTElN 2,261,350

ELECTRIC RESISTANCE HEATING UNIT Filed May 8, 1940 FIG.4.

INVENTOR. m MILTON EPSTEIN m BY f0 9 no.5. 2 W$4MW ATTORNEY.

Patented Nov. 4, 1941 ELECTRIC RESISTANCE HEATING UNIT Milton Epstein, St. Louis, Mo., assignor to Industrial Engineering & Equipment 00., St. Louis, Mo., a corporation of Missouri Application May 8, 1940, Serial No. 333,913

3 Claims.

My invention relates to electric resistance heating units and more particularly to improvements in units of this character having the form of a flat, elongated plate.

The principal object of my invention is to provide an improved heating unit which is especially, although not exclusively adapted for use in connection with wrapping machines as a means for thermo-plasticizing the adhesive agent carried by the wrapping material.

An important objective of the invention is attained in a heating unit embodying certain improved features of construction that render it impervious to oils, paraliins or other highly penetrating substances that are deleterious to the electrical resistance element of the unit and with which certain types of wrapping material are impregnated.

Another object resides in the provision of a heating unit of the character described, embodying an improved electrical terminal assembly that makes for safety and convenience of installation.

Other objects are attained in constructional features directed generally to increasing the sturdiness, durability and useful life of the unit.

The invention will be understood from the following detailed description and accompanying drawing of a preferred embodiment of my invention, Fig. 1 of which is a perspective view of an assembled unit; Fig. 2 is an exploded perspective view showing component parts of the terminal assembly; Fig. 3 is a plan View of the unit with portions thereof broken away to illustrate the construction and arrangement of interior parts; Fig. 4 is a longitudinal sectional View taken at line 4-4 of Fig. 3, and Fig. 5 is a transverse sectional view taken at line 5-5 of Fig. 3.

Referring now to the drawing, the heating unit of my invention includes a relatively flat, elongated casing member 5, rectangular in cross-section, the casing member being preferably formed of seamless brass tubing of the shape aforesaid. Pro-formed tubing of seamless brass for the easing is preferred to other structural forms and metals heretofore employed for a like purpose, such as cast aluminum, because of the fact that it is substantially non-porous and impervious to paraffin oil or other substances that can penetrate casings of metal having coarser grain structure.

At one end of the casing 5 the upper wall 6 thereof together with adjacent portions of the narrow side walls 1 are removed whereby to provide an upper opening for access to the terminal block 8, hereinafter more fully described. Disposed within the casing 5 is a preformed core member 9 of suitable refractory material, such core being shaped to fit snugly within the casing and of length to extend from one end thereof substantially to the inner end of the terminal block 8 near the opposite end of the casing. The refractory core 9 may be formed as an integral unit as shown, or may consist of a plurality of short sections disposed in end abutting relation. Extending longitudinally of the core member are a plurality of laterally spaced passages or bores I 6. each of which is adapted to receive one span of the coiled electric heating element l I. In the present example the spans or sections of the heating element H are interconnected at their corresponding ends in series circuit relation, the cross portions l2 that connect adjacent spans traversing the ends of the ribs l3 that intervene the bores. The terminal ends H! of the heating element are located at the opposite, outermost bores and project outwardly therefrom for securement to conducting bars l5 of the terminal assembly.

The terminal assembly includes the block 8 previously referred to which is desirably formed of an insulating refractory material such as lava. Block 8 is provided with longitudinal passages l5 appropriately spaced to communicate with the outer bores of the core member 9, the passages l6 extending from the inner end face ll of the block to points short of its outer end face 18. Further, block 8 is recessed at its outer end to provide a horizontal step l9 lying in a plane that passes through the axes of passages 16. The conducting or terminal bars l5 are disposed in passages l6 and are preferably formed of round brass rod stock, the opposite end portions in and 2| of the terminal members l5 being milled to half-round section as shown. Each of these end portions has a threaded recess for the reception of screws 22 and 23 that constitute binding posts. The ends M of the heating element are secured to the terminal bars by the screws 23, and in assembly-this connection is concealed within the passages I6. The terminal screws 22 at the outer ends of the terminal bars are presented at the recessed portion of the terminal block whereby they are readily accessible for connection with external conductor leads A.

In assembly, after the ends M of the heating element are secured to the terminal bars and these members positioned in the passages l6, said passages are packed with non-conductive cement, indicated at 24, which serves to immobilize the terminal bars and to prevent extraneous fluids or the like from entering the casing through said passages.

As will appear, the inner end portion of the terminal block 8 projects a substantial distance into the end of the casing, fitting snugly therein. The said block is provided with a ridge or shoulder adapted to fit against the end edge 26 of the upper casing wall 6, the upper surface of the shoulder 25 being flush with the upper wall surface. A relatively thin mica plate 21 is cemented in place between the lapping surfaces of the upper casing wall and the terminal block, and a second mica plate 210. is disposed against the inner end face of the terminal block, the plate 21a having openings for the passage therethrough of the ends 14 of the heating element. Cement is further employed as a seal between all other mating surfaces of the terminal block and casing, including the crevice between the end edge 26 of the upper casing wall and the shoulder 25 on the terminal block. The mica plates 21 and 21a function in the manner of resilient packing and expand and contract in accordance with corresponding changes in the metal casing, due to thermal effects, whereby to prevent the occurrence of air pockets in the casing or impairment of the seal between the casing and terminal member. The effectiveness of the oil-excluding seal at the zone where the casing is most vulnerable is further augmented by the shoulder 25 on the terminal block.

A screw 28 in conjunction with the aforesaid cement bond or seal serves to secure the terminal block to the casing, such screw extending through apertures in the upper casing wall and terminal block and engaging a threaded aperture in the bottom casing wall.. The terminal screws 22 and all exposed metal parts of the terminal assembly are normally covered and protected by a removable cap 29 of suitable insulating material. Cap 29 fits the stepped recess of the terminal block and is provided in its under surface with grooves 30 to receive the terminal screws 22 and conductors A, leading thereto. Cap 29 is secured in place by means of a short metal strip 3| attached to the casing by the screw 28, said strip projecting over cap 29. A screw 32 extending through a tapped opening in strip 3| and into an aperture in the protector cap 29 serves to position the said cap on the terminal block.

After all of the parts are assembled as above described magnesium oxide powder is introduced into the casing through the open end 33 thereof, such powder completely filling all openings and crevices in and around the core member 9, and embedding the resistance element I I. The packing of the magnesium oxide powder as aforesaid is desirably accomplished by well known vibration methods. Thus, the unit is subjected to vibration until the powder becomes crammed in all interior spaces or crevices, to the end of eliminating all air pockets. Thereafter a mica plate 34 is placed over the magnesium oxide powder covering the end of the core member and the casing is closed by a metal end plate 35 marginally secured as by silver solder to the end edges of the casing walls.

Although I have described for purposes of illustration a presently preferred embodiment of my invention, it will be understood that various changes may be made in the unit described herein without departing from the spirit and full intendment of the invention which is defined by the appended claims.

I claim:

1. In an electric resistance heating unit, a flat, elongated metal casing having top, bottom, sides and one end wall, a pro-formed core member of refractory material snugly fitting the interior of said casing and having a resistance element embedded therein, a terminal and closure assembly for said casing comprising a block of insulating material extending into and snugly fitting the open end of the casing, said block having a shoulder abutting the forward edge of the casing top wall, a mica plate cemented to and between the lapping surfaces of said block and the casing top wall, said block further having a forwardly projecting shelf portion spaced below its upper surface, and a plurality of longitudinal passages in said block, said passages continuing as grooves in the upper surface of said shelf portion, conductor rods in said passages, said rods having flattened terminal portions seated in said grooves substantially flush with the upper surface of said shelf, bonding means in said passages forming a seal about said rods, terminal screws in said flattened r'od portions for connecting conductor leads thereto, means connecting said rods to the ends of said resistance element, and an insulating cap detachably mounted on the shelf portion of said terminal block, providing a protecting cover for all exposed metal parts of the terminal assembly.

2. In an electric resistance heating unit, a flat, elongated casing formed of sheet metal and having top, bottom, sides and one end wall, said bottom wall projecting beyond the forward edge of the upper wall at the open end of the casing; a terminal block of insulating material extending into and forming a plug-like closure for the open end of said casing, the upper surface of said terminal block being recessed to form a shoulder for abutting engagement with the forward edge of the casing top wall, said block further having a stepped recess at its forward end for terminal connections, longitudinal bores formed in said block, said bores opening into said forward recess and terminating short of the forward edge of the block, conductor rods ensconced in said bores, terminal screws for clamping external lead conductors to the upper, exposed surfaces of said rods, a removable protector cap of insulating material formed to fit said terminal recess of said block and to cover the exposed metal parts of the terminal assembly; means forming a fluidexcluding seal in and about said terminal block, including mica packing cemented in place between adjacent mating surfaces of the casing and terminal block and a cement filler embedding said conductor rods in the bores of said terminal block; a pro-formed core member of refractory material in said casing, said core member having longitudinal passages therein, a resistance heating element extending through said passages, means connecting the ends of said element each to one of said conductor rods, and a powdered magnesium oxide filler in and about said core member.

3. In an electrical heating unit, a flat, elongated metal casing, a core member of refractory material in said casing, said core member having a resistance heating wire embedded therein, a terminal assembly comprising a block of insulating material fitting snugly within one end of the casing to provide a closure therefor, said terminal block having a shelf portion projecting forwardly beyond, and spaced below the plane of the top wall of the casing, a plurality of longitudinal passages in said block, conductor bars sealed within said passages and projecting forwardly on said shelf portion, terminal screws threaded transversely in the projecting forward ends of said conductor bars, means connecting said bars to the ends of said resistance heating wire, and an insulating cap detachably mounted on the shelf portion of the terminal block, said cap having longitudinal channels in its under surface to accommodate said terminal screws and current supply conductors, said cap providing at protecting cover for all exposed, live metal parts of the terminal assembly.

MILTON EPSTEIN. 

